Tolls charged for the use of automobile toll highways may vary according to certain factors, such as vehicle weight and a number of axles per vehicle, for example. Because tolls vary based on such factors, it is necessary to obtain information about vehicles as they pass through toll plazas to ensure that proper fares are charged.
Currently, a number of axles of vehicles moving through toll plazas may be determined through one or more sets of electrical contact switches located in one or more treadles located in the path of oncoming traffic as they pass through these plazas. Such treadles are typically arranged such that their longitudinal dimensions are substantially orthogonal to a direction of traffic. Also, treadles may be located in a cavity of a roadbed such that an upper surface of the treadle is substantially level with a surface of the roadbed. Alternatively, the treadles may be located on a surface of the roadbed with their top surfaces being slightly elevated from the surface of the roadbed. The electrical contact switches in the treadle are activated by a weight of a vehicle as it passes over the treadle. As depicted in FIGS. 1-3, a contact switch system 5 includes a first conductive strip 10 and a second conductive strip 20 separated by a space 30 and held in a rubber jacket 40 of a treadle 41 to maintain such a space or air gap between the conductive strips. As a vehicle passes over rubber jacket 40, first conductive strip 10 descends due to the weight of the vehicle and abuts second conductive strip 30. Each electrical contact of the conductive strips may be counted to allow a determination of a number of axles which cross the treadle in a certain period of time. Such electrical contact switches may thus allow the classification of vehicles based on the number of axles passing over such treadles.
Other examples of mechanisms for classifying vehicles include optical recognition devices, vehicle separation sensors, scales for weighing vehicles, and speed detection devices. The need for such devices has increased due to the advent of automatic RF (Radio Frequency) Electronic Toll Collection systems (e.g., EZ PASS, FASTLANE) which collect tolls electronically from a user's account without the necessity of the vehicle stopping at the toll plaza. However, some of these mechanisms require extensive renovations and/or road construction at such toll plazas for their installation.
Thus, a need exists for a system for determining a classification of a moving vehicle at toll collection plazas which utilizes existing assets of such plazas and does not require extensive renovations of the plazas.